| OAuth Working Group | M. Jones |
| Internet-Draft | Microsoft |
| Intended status: Standards Track | P. Hunt |
| Expires: July 23, 2017 | Oracle |
| January 19, 2017 |
OAuth 2.0 Protected Resource Metadata
draft-jones-oauth-resource-metadata-01
This specification defines a metadata format that an OAuth 2.0 client can use to obtain the information needed to interact with an OAuth 2.0 protected resource.
This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."
This Internet-Draft will expire on July 23, 2017.
Copyright (c) 2017 IETF Trust and the persons identified as the document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.
This specification defines a metadata format enabling OAuth 2.0 clients to obtain information needed to interact with an OAuth 2.0 protected resource. This specification is intentionally as parallel as possible to "OAuth 2.0 Dynamic Client Registration Protocol" [RFC7591], which enables a client to provide metadata about itself to an OAuth 2.0 authorization server and to OAuth 2.0 Authorization Server Metadata [OAuth.AuthorizationMetadata], which enables a client to obtain metadata about an OAuth 2.0 authorization server.
The metadata for a protected resource is retrieved from a well-known location as a JSON [RFC7159] document, which declares information about its capabilities and optionally, its relationships to other services. This process is described in Section 3.
This metadata can either be communicated in a self-asserted fashion or as a set of signed metadata values represented as claims in a JSON Web Token (JWT) [JWT]. In the JWT case, the issuer is vouching for the validity of the data about the protected resource. This is analogous to the role that the Software Statement plays in OAuth Dynamic Client Registration [RFC7591].
Each protected resource publishing metadata about itself makes its own metadata document available at a well-known location rooted at the protect resource's URL, even when the resource server implements multiple protected resources. This prevents attackers from publishing metadata supposedly describing the protected resource, but that is not actually authoritative for the protected resource, as described in Section 6.2.
The means by which the client obtains the location of the protected resource metadata document is out of scope. In some cases, the location may be manually configured into the client. In other cases, it may be dynamically discovered, for instance, through the use of WebFinger [RFC7033], in a manner related to the description in Section 2 of "OpenID Connect Discovery 1.0" [OpenID.Discovery].
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119].
All uses of JSON Web Signature (JWS) [JWS] and JSON Web Encryption (JWE) [JWE] data structures in this specification utilize the JWS Compact Serialization or the JWE Compact Serialization; the JWS JSON Serialization and the JWE JSON Serialization are not used.
This specification uses the terms "Access Token", "Authorization Code", "Authorization Endpoint", "Authorization Grant", "Authorization Server", "Client", "Client Authentication", "Client Identifier", "Client Secret", "Grant Type", "Protected Resource", "Redirection URI", "Refresh Token", "Resource Owner", "Resource Server", "Response Type", and "Token Endpoint" defined by OAuth 2.0 [RFC6749], the terms "Claim Name", "Claim Value", and "JSON Web Token (JWT)" defined by JSON Web Token (JWT) [JWT].
Protected resources can have metadata describing their configuration. The following protected resource metadata values are used by this specification and are registered in the IANA "OAuth Protected Resource Metadata" registry established in Section 7.1:
Additional protected resource metadata parameters MAY also be used.
In addition to JSON elements, metadata values MAY also be provided as a signed_metadata value, which is a JSON Web Token (JWT) [JWT] that asserts metadata values about the protected resource as a bundle. A set of claims that can be used in signed metadata are defined in Section 2. The signed metadata MUST be digitally signed or MACed using JSON Web Signature (JWS) [JWS] and MUST contain an iss (issuer) claim denoting the party attesting to the claims in the signed metadata. Consumers of the metadata MAY ignore the signed metadata if they do not support this feature. If the consumer of the metadata supports signed metadata, metadata values conveyed in the signed metadata MUST take precedence over those conveyed using plain JSON elements.
Signed metadata is included in the protected resource metadata JSON object using this OPTIONAL member:
Protected resources supporting metadata MUST make a JSON document containing metadata as specified in Section 2 available at a path formed by concatenating a well-known URI string such as /.well-known/oauth-protected-resource to the protected resource's resource identifier. The syntax and semantics of .well-known are defined in RFC 5785 [RFC5785]. The well-known URI path suffix used MUST be registered in the IANA "Well-Known URIs" registry [IANA.well-known].
Different applications utilizing OAuth protected resources in application-specific ways may define and register different well-known URI path suffixes used to publish protected resource metadata as used by those applications. For instance, if the Example application uses an OAuth protected resource in an Example-specific way, and there are Example-specific metadata values that it needs to publish, then it might register and use the example-resource-configuration URI path suffix and publish the metadata document at the path formed by concatenating /.well-known/example-resource-configuration to the protected resource's resource identifier.
An OAuth 2.0 application using this specification MUST specify what well-known URI string it will use for this purpose. The same protected resource MAY choose to publish its metadata at multiple well-known locations relative to its resource identifier, for example, publishing metadata at both /.well-known/example-resource-configuration and /.well-known/oauth-protected-resource.
A protected resource metadata document MUST be queried using an HTTP GET request at the previously specified path.
The consumer of the metadata would make the following request when the resource identifier is https://resource.example.com and the well-known URI path suffix is oauth-protected-resource to obtain the metadata, since the resource identifier contains no path component:
GET /.well-known/oauth-protected-resource HTTP/1.1 Host: resource.example.com
If the resource identifier value contains a path component, any terminating / MUST be removed before appending /.well-known/ and the well-known URI path suffix. The consumer of the metadata would make the following request when the resource identifier is https://resource.example.com/resource1 and the well-known URI path suffix is oauth-protected-resource to obtain the metadata, since the resource identifier contains a path component:
GET /resource1/.well-known/oauth-protected-resource HTTP/1.1 Host: resource.example.com
Using path components enables supporting multiple resources per host. This is required in some multi-tenant hosting configurations. This use of .well-known is for supporting multiple resources per host; unlike its use in RFC 5785 [RFC5785], it does not provide general information about the host.
The response is a set of claims about the protected resource's configuration. A successful response MUST use the 200 OK HTTP status code and return a JSON object using the application/json content type that contains a set of claims as its members that are a subset of the metadata values defined in Section 2. Other claims MAY also be returned.
Claims that return multiple values are represented as JSON arrays. Claims with zero elements MUST be omitted from the response.
An error response uses the applicable HTTP status code value.
The following is a non-normative example response:
HTTP/1.1 200 OK
Content-Type: application/json
{
"resource":
"https://resource.example.com",
"authorization_servers":
["https://as1.example.com",
"https://as2.example.net"],
"bearer_methods_supported":
["header", "body"],
"resource_documentation":
"http://resource.example.com/resource_documentation.html"
}
The resource value returned MUST be identical to the protected resource's resource identifier value that was concatenated with the well-known URI path suffix to create the URL used to retrieve the metadata. If these values are not identical, the data contained in the response MUST NOT be used.
To support use cases in which the set of legitimate protected resources to use with the authorization server is fixed and enumerable, this specification defines the protected_resources metadata value, which enables explicitly listing them. Note that if the set of legitimate authorization servers to use with a protected resource is also fixed and enumerable, lists in the authorization server metadata and protected resource metadata should be cross-checked against one another for consistency when these lists are used by the application profile.
The following authorization server metadata value is defined by this specification and is registered in the IANA "OAuth Authorization Server Metadata" registry established in OAuth 2.0 Authorization Server Metadata [OAuth.AuthorizationMetadata].
Processing some OAuth 2.0 messages requires comparing values in the messages to known values. For example, the member names in the metadata response might be compared to specific member names such as resource. Comparing Unicode [UNICODE] strings, however, has significant security implications.
Therefore, comparisons between JSON strings and other Unicode strings MUST be performed as specified below:
Implementations MUST support TLS. Which version(s) ought to be implemented will vary over time, and depend on the widespread deployment and known security vulnerabilities at the time of implementation. The protected resource MUST support TLS version 1.2 [RFC5246] and MAY support additional transport-layer security mechanisms meeting its security requirements. When using TLS, the client MUST perform a TLS/SSL server certificate check, per RFC 6125 [RFC6125]. Implementation security considerations can be found in Recommendations for Secure Use of TLS and DTLS [BCP195].
To protect against information disclosure and tampering, confidentiality protection MUST be applied using TLS with a ciphersuite that provides confidentiality and integrity protection.
TLS certificate checking MUST be performed by the client, as described in Section 6.1, when making a protected resource metadata request. Checking that the server certificate is valid for the resource identifier URL prevents man-in-middle and DNS-based attacks. These attacks could cause a client to be tricked into using an attacker's resource server, which would enable impersonation of the legitimate protected resource. If an attacker can accomplish this, they can access the resources that the affected client has access to using the protected resource that they are impersonating.
An attacker may also attempt to impersonate a protected resource by publishing a metadata document that contains a resource claim using the resource identifier URL of the protected resource being impersonated, but containing information of the attacker's choosing. This would enable it to impersonate that protected resource, if accepted by the client. To prevent this, the client MUST ensure that the resource identifier URL it is using as the prefix for the metadata request exactly matches the value of the resource metadata value in the protected resource metadata document received by the client.
Publishing information about the protected resource in a standard format makes it easier for both legitimate clients and attackers to use the protected resource. Whether a protected resource publishes its metadata in an ad-hoc manner or in the standard format defined by this specification, the same defenses against attacks that might be mounted that use this information should be applied.
Secure determination of appropriate authorization servers to use with a protected resource for all use cases is out of scope of this specification. This specification assumes that the client has a means of determining appropriate authorization servers to use with a protected resource and that the client is using the correct metadata for each protected resource. Implementers need to be aware that if an inappropriate authorization server is used by the client, that an attacker may be able to act as a man-in-the-middle proxy to a valid authorization server without it being detected by the authorization server or the client.
The ways to determine the appropriate authorization servers to use with a protected resource are in general, application-dependent. For instance, some protected resources are used with a fixed authorization server or set of authorization servers, the locations of which may be well known, or which could be published as metadata values by the protected resource. In other cases, the set of authorization servers that can be used with a protected resource can by dynamically changed by administrative actions or by changes to the set of authorization servers adhering to a trust framework. Many other means of determining appropriate associations between protected resources and authorization servers are also possible.
To support use cases in which the set of legitimate authorization servers to use with the protected resource is fixed and enumerable, this specification defines the authorization_servers metadata value, which enables explicitly listing them. Note that if the set of legitimate protected resources to use with an authorization server is also fixed and enumerable, lists in the protected resource metadata and authorization server metadata should be cross-checked against one another for consistency when these lists are used by the application profile.
The following registration procedure is used for the registry established by this specification.
Values are registered on a Specification Required [RFC5226] basis after a two-week review period on the oauth-ext-review@ietf.org mailing list, on the advice of one or more Designated Experts. However, to allow for the allocation of values prior to publication, the Designated Experts may approve registration once they are satisfied that such a specification will be published.
Registration requests sent to the mailing list for review should use an appropriate subject (e.g., "Request to register OAuth Protected Resource Metadata: example").
Within the review period, the Designated Experts will either approve or deny the registration request, communicating this decision to the review list and IANA. Denials should include an explanation and, if applicable, suggestions as to how to make the request successful. Registration requests that are undetermined for a period longer than 21 days can be brought to the IESG's attention (using the iesg@ietf.org mailing list) for resolution.
Criteria that should be applied by the Designated Experts includes determining whether the proposed registration duplicates existing functionality, determining whether it is likely to be of general applicability or whether it is useful only for a single application, and whether the registration makes sense.
IANA must only accept registry updates from the Designated Experts and should direct all requests for registration to the review mailing list.
It is suggested that multiple Designated Experts be appointed who are able to represent the perspectives of different applications using this specification, in order to enable broadly-informed review of registration decisions. In cases where a registration decision could be perceived as creating a conflict of interest for a particular Expert, that Expert should defer to the judgment of the other Experts.
This specification establishes the IANA "OAuth Protected Resource Metadata" registry for OAuth 2.0 protected resource metadata names. The registry records the protected resource metadata member and a reference to the specification that defines it.
The following authorization server metadata value is registered in the IANA "OAuth Authorization Server Metadata" registry established in OAuth 2.0 Authorization Server Metadata [OAuth.AuthorizationMetadata].
This specification registers the well-known URI defined in Section 3 in the IANA "Well-Known URIs" registry [IANA.well-known] established by RFC 5785 [RFC5785].
| [I-D.ietf-oauth-mix-up-mitigation] | Jones, M., Bradley, J. and N. Sakimura, "OAuth 2.0 Mix-Up Mitigation", Internet-Draft draft-ietf-oauth-mix-up-mitigation-01, July 2016. |
| [IANA.well-known] | IANA, "Well-Known URIs" |
| [OpenID.Discovery] | Sakimura, N., Bradley, J., Jones, M. and E. Jay, "OpenID Connect Discovery 1.0", November 2014. |
Thanks to George Fletcher and Tony Nadalin for their input on the specification.
[[ to be removed by the RFC Editor before publication as an RFC ]]
-01
-00